The present invention relates to a method of determining the remaining lifetime of contacts in switchgear, in particular contractor contacts. The present invention also relates to the respective arrangement for carrying out the method, with an analyzer unit for displaying the remaining lifetime.
In German Patent Application No. 44 27 066 (not prior art), the remaining lifetime of a contactor in the shutdown cycle is derived from the difference in time between the start of the armature opening movement and the start of contact opening. Using an analysis algorithm, a microprocessor then determines from the time difference value the present value of the contact spring action, which decreases from its value when new (=100% remaining lifetime) to its minimum value (=0% remaining lifetime) due to contact erosion. The time signals required for this are detected first by interrupting an auxiliary circuit over the armature and yoke of the solenoid actuator and also by the contact voltage at the main contacts and are converted to well-defined voltage pulses, for which purpose measuring leads must be attached.
Attaching measuring leads (six leads for three-phase current) for analysis of contact voltages may be problematical inasmuch as
a) the possibility of vagabond voltage forming from the infeed side to the load side of the contactor cannot be ruled out,
b) the required insulation voltage endurance (8 kV) results in a higher cost for the analysis circuit, and
c) integrating the measuring leads into the contactor and connecting them to a plug-in connector necessitates design and safety-related changes.
An object of the present invention is to provide a method and the respective arrangement, wherein the start of contact opening need not be determined over measuring leads on both the feed and load ends of the main circuit.
This object is achieved according to the present invention by measured value acquisition on the contact gap on the load side of the monitored switching device and by voltageless signaling of the start of armature movement. For use in three-phase systems, the start of contact opening of the contact points with the greatest erosion of one of the switching poles is preferably detected by measuring the switching voltage as the change in voltage at an artificial neutral point on the load side of the switching device monitored, from which it is then possible to determine the remaining lifetime of the main contacts of the contactor in addition to the start of armature movement.
In the respective arrangement with an analyzer unit for displaying the remaining lifetime, there is a voltageless signal line on the armature and yoke of the solenoid actuator of the switching device between the switching device and the analyzer unit. The analyzer unit is thus located between the switching device and the electric consumer on the load side.
To reduce the technical complexity, it is thus no longer necessary to monitor each main circuit individually with regard to contact erosion in three-phase systems in particular, but instead only the spring action of the most eroded contacts of one of the three switching poles is measured to determine the remaining lifetime of the main contacts of the contactor. Furthermore, it is possible to determine the remaining lifetime without a strict spatial correlation with the contactor, the start of the armature opening movement being signaled to the analyzer unit over a voltageless signal line as contact interruption between armature and yoke.
Voltageless signaling in the aforementioned context is understood to refer to electric contacting between armature and yoke, in contrast with a voltage signal, such as the contact voltage on the main contacts.